Oligonucleotides are useful in therapeutic, diagnostic, research, and new and nanomaterials applications. The use of natural sequences of DNA or RNA is limited, for example, by their stability to nucleases. Additionally, in vitro studies have shown that the properties of antisense nucleotides such as binding affinity, sequence specific binding to the complementary RNA, stability to nucleases are affected by the configurations of the phosphorous atoms. Therefore, there is a need for prodrugs of stereodefined oligonucleotides to impart additional stability to oligonucleotide molecules in a number of in-vitro and in-vivo applications Prodrugs of stereodefined oligonucleotides which comprise phosphorus atom-modified nucleic acids and methods of use thereof are described herein.